Carbon nanostructures are a new class of materials that potentially have a wide range of applications. Typically, carbon nanostructures have a length from about 0.01 mm to about 0.1 mm and have a diameter of about 10 nm to about 100 nm. Carbon nanostructures, such as carbon nanotubes, have a unique combination of properties that may allow the development of new products and improvements in existing products. Potential applications for carbon nanostructures include microelectronics, scanning probes and sensors, field emission devices such as video and computer displays and nanoelectronics. Most-promising near-term applications include electromagnetic shielding and electron field emission displays for computers and other high-tech devices and in applications requiring improved heat transfer and thermal insulation properties. Longer range target applications include photovoltaics, supercapacitors, batteries, fuel cells, computer memory, carbon electrodes, carbon foams, actuators, materials for hydrogen storage, adsorbants and as supports. Carbon nanotubes have such wide applicability due to their many unique mechanical, electrical and chemical properties. These properties include electrical conductivity, mechanical strength and thermal conductivity. For instance, carbon nanotubes may have mechanical strength of 10 to 100 times the strength of steel, but at a fraction of the weight. Carbon nanotubes additionally demonstrate remarkably consistent electrical behavior. In fact, they exhibit an essentially metallic behavior and conduct electricity over well-separated electronic states while remaining coherent over the distances needed to interconnect various molecular computer components. Therefore, a wire produced from carbon nanotubes may potentially be used to connect molecular electronic components.
Carbon nanostructures may be produced in many different morphologies, including single walled tubes, multiwalled tubes, ribbons, sheets, as well as more complex morphologies. Strong van der Waals attraction forces additionally allow spontaneous roping of nanostructures leading to the formation extended carbon based structures.
Presently, there are several different process for the preparation of carbon nanotubes. Nanotubes may produced on a limited scale by a process utilizing arc discharge as described by Ebbesen, T. W.; Ajayan, P. M.; Nature (London), 1992; Vol. 358, pp 220–222; Iijima, S. In Nature (London), 1991; Vol. 354, pp 56–58; Bethune, D. S.; Kiang, C. H.; de Vries, M. S.; Gorman, G.; Savoy, R.; Vazquez, J.; Beyers, R.; Nature (London), 1993; Vol. 363, pp 605–607; Iijima, S.; Ichihashi, T.; Nature 1993, 363, 603–605; a process comprising laser ablation is described by Rinzler, A. G.; Liu, J.; Dai, H.; Nikolaev, P.; Huffman, C. B.; Rodriguez-Macias, F. J.; Boul, P. J.; Lu, A. H.; Heymann, D.; Colbert, D. T.; Lee, R. S.; Fischer, J. E.; Rao, A. M.; Eklund, P. C.; Smalley, R. E. In Appl. Phys. A: Mater. Sci. Process., 1998; Vol. A67, pp 29–37; Thess, A.; Lee, R.; Nikolaev, P.; Dai, H.; Petit, P.; Robert, J.; Xu, C.; Lee, Y. H.; Kim, S. G.; Rinzler, A. G.; Colbert, D. T.; Scuseria, G. E.; Tomanek, D.; Fischer, J. E.; Smalley, R. E. Science 1996, 273, 483–487; by pyrolysis of bulk polymers by Cho, W.-S.; Hamada, E.; Kondo, Y.; Takayanagi, K.; Appl. Phys. Lett., 1996; Vol. 69, pp 278–279; U.S. Pat. No. 6,156,256 describes the production of carbon nanofibers directly from hydrocarbons in a gas phase reaction upon contact with a catalytic metal particle when heated to about 1000° C. in a non-oxidizing gas stream; and a process comprising the chemical vapor deposition (CVD) of carbon by Jose-Yacaman, M.; Miki-Yoshida, M.; Rendon, L.; Santiesteban, J. G. In Appl. Phys. Lett., 1993; Vol. 62, pp 657–659; Ren, Z. F.; Huang, Z. P.; Xu, J. W.; Wang, J. H.; Bush, P.; Siegal, M. P.; Provencio, P. N. Science 1998, 282, 1105–1107; Huang, S.; Mau, A. W. H.; Turney, T. W.; White, P. A.; Dai, L. In J. Phys. Chem. B, 2000; Vol. 104, pp 2193–2196; Huang, S.; Dai, L.; Mau, A. W. H. In J. Phys. Chem. B, 1999; Vol. 103, pp 4223–4227.
The CVD processes have also been used to prepare ordered arrays of carbon nanotubes, Xie, S. S.; Chang, B. H.; Li, W. Z.; Pan, Z. W.; Sun, L. F.; Mao, J. M.; Chen, X. H.; Qian, L. X.; Zhou, W. Y. In Adv. Mater. (Weinheim, Ger.), 1999; Vol. 11, pp 1135–1138; Rohmund, F.; Falk, L. K. L.; Campbell, E. E. B. In Chem. Phys. Lett., 2000; Vol. 328, pp 369–373; Fan, S.; Liang, W.; Dang, H.; Franklin, N.; Tombler, T.; Chapline, M.; Dai, H. Physica E (Amsterdam), 2000; Vol. 8, pp 179–183; Wang, Q. H.; Setlur, A. A.; Lauerhaas, J. M.; Dai, J. Y.; Seelig, E. W.; Chang, R. P. H. In Appl. Phys. Lett., 1998; Vol. 72, pp 2912–2913.
Carbon nanotubes are structures that consist of a sheet of carbon atoms in graphene form wrapped into a cylinder. A single walled nanotube (SWNT) has only a single atomic layer of carbon atoms whereas multiwalled nanotubes (MWNT) may comprise of up to a thousand cylindrical graphene layers. MWNTs have excellent strength, small diameter (typically less than 200 nm) and near-metallic electrical conductivity, making them useful as an additive to enhance structural properties of composites such as carbon-carbon, carbon-epoxy, carbon-metal, carbon-plastic, carbon-polymer and carbon-concrete.
The physical, electrical and chemical properties of carbon nanostructures strongly depend on the size and topology of the nanotubes as well as the uniformity of these dimensions. Alignment of the carbon nanotubes is particularly important for their use in many applications, such as flat panel displays.
There exists a need for a more robust method of producing a wide variety of uniform carbon nanostructured materials economically.
There is a need for a nanostructure material having a high surface area layer containing uniform pores with a high effective surface area, and thus increasing the number of potential chemical reaction or catalysis sites on the nanostructure, which may also be functionalized to enhance chemical activity.
There is a further need to provide a composition of matter comprising a nanofiber having an activated high surface area layer containing additional pores and additional functionality which increase the effective surface area of the nanofiber and increase the number of potential chemical reaction or catalysis sites on the nanofiber, which is functionalized to enhance chemical activity wherein the additional functionality comprises a transition metal. Such a material has just been discussed in WO 02/16680 but that material does not teach how to control the diameter of the pores within nanofibers nor the surface area of the carbon nanostructured materials.
A still a further need is to provide a composition of matter comprising a nanofiber or nanostructured material comprising a carbide. A further need is a free standing carbon based article with uniformly distributed porosity. Of particular interest would be materials with nanopores of predeterminable diameters.
In addition, unless otherwise indicated, all numbers expressing quantities of ingredients, compositions, time, temperatures, distances and so forth used in the present specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the method of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practical. Any numerical value, however, may inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
The reader will appreciate the details and advantages of the present invention, as well as others, upon consideration of the following description of embodiments of the invention. The reader also may comprehend such additional details and advantages of the present invention upon performing the method and using the nanostructured materials of the present invention.